The present invention relates generally to semiconductor manufacturing and, more particularly, to methods for testing semiconductor dice having raised or bumped bond pads. More particularly still, the present invention relates to fabricating and using a testing grid suitable for testing solder balls used for bumped bond pads on an unpackaged semiconductor die.
Semiconductor dice are being fabricated with raised bond pads and are known as bumped semiconductor die. A bumped semiconductor die includes bond pads along with bumped solderable material such as a lead-tin alloy. These typically are manufactured from solder balls made of a lead-tin alloy. Bumped dies are often used for flip-chip bonding where the die is mounted face down on the substrate, such as a printed circuit board, and then the die is attached to the substrate by welding or soldering. Typically, the bumps are formed as balls of materials that are circular in a cross-sectional plane parallel to the face of the die. The bumps typically have a diameter of from 50 micrometers (μm) to 100 μm. The sides of the bumps typically bow or curve outwardly from a flat top surface. The flat top surface forms the actual region of contact with a mating electrode on the printed circuit board or other substrate. In testing the attached solder bumps, a temporary electrical connection must be made between the ball contact locations or bond pads on the die and the external test circuitry associated with the testing apparatus. The bond pads provide a connection point for testing an integrated circuit on the die. Likewise, the integrity of each bump must be tested as well.
In making this temporary electrical connection, it is desirable to effect a connection that causes as little damage as possible to the bumped die. If the temporary connection to the bumped bond pad damages the pad, the entire die may be ruined. This is difficult to accomplish because the connection must also produce a low resistance or ohmic contact with the bumped bond pad. A bond pad, with or without a bump, typically has a metal oxide layer formed over it that must be penetrated to make the ohmic contact.
Some prior art contact structures, such as probe cards, scrape the bond pads and wipe away the oxide layer. This causes excess layer damage to the bond pads. Other interconnect structures, such as probe tips, may pierce the oxide layer and metal bond pad and leave a deep gouge. Still other interconnect structures, such as micro bumps, cannot even pierce the oxide layer, preventing the formation of an ohmic contact.
In the past, following testing of a bump pad die, it has been necessary to reflow the bumps, which are typically damaged by the procedure. This is an additional process step that adds to the expense and complexity of the testing process. Furthermore, it requires heating the tested die that can adversely affect the integrated circuitry formed on the die.
Other bond pad integrity testing systems have been developed in the prior art. Typically, these testing systems use optical imaging to determine the integrity of the weld connection on the bumped sites. One type of system is a profiling system that uses interferometry with robotic wafer handling to automate the testing step. The testing step develops a profile for measuring solder bump heights. Unfortunately, although the interferometry system does not damage the device in any way, the time required for analyzing each bump location can take from two to four minutes. This type of throughput is unacceptable when a high speed system is necessary.
Accordingly, what is needed is a method and system for testing solder bumps in bond pad locations that does not damage the bond pads while improving throughput.